- Michael R Law, research fellow1,
- Sumit R Majumdar, associate professor2,
- Stephen B Soumerai, professor1
- 1Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, 133 Brookline Avenue, 6th floor, Boston, MA 02215, USA
- 2Division of General Internal Medicine, Department of Medicine, 2E3.07 Walter Mackenzie Health Sciences Centre, University of Alberta Hospital, Edmonton, Alberta T6G 2B7, Canada
- Correspondence to: M R Law
- Accepted 19 June 2008
Objective To assess the impact of direct to consumer advertising of prescription drugs in the United States on Canadian prescribing rates for three heavily marketed drugs—etanercept, mometasone, and tegaserod.
Design Controlled quasi-experimental study using interrupted time series analysis.
Population Representative sample of 2700 Canadian pharmacies and prescription data from 50 US Medicaid programmes.
Main outcome measures Differences in number of filled prescriptions per 10 000 population per month between English speaking and French speaking (control) Canadian provinces before and after the start of direct to consumer advertising in the United States.
Results Spending on direct to consumer advertising for study drugs ranged from $194m to $314m (£104m-£169m; €131m-€212m) over the study period. Prescription rates for etanercept and mometasone did not increase in English speaking provinces relative to French speaking controls after the start of direct to consumer advertising. In contrast, tegaserod prescriptions increased 42% (0.56 prescriptions/10 000 residents, 95% confidence interval 0.37 to 0.76) in English speaking provinces immediately after the start of US direct to consumer advertising. Uncontrolled analysis of US Medicaid data showed a larger 56% increase in tegaserod prescriptions. However, this increase did not persist over time in either country, despite continued advertising.
Conclusions Exposure to US direct to consumer advertising transiently influenced both Canadian and US prescribing rates for tegaserod, a drug later withdrawn owing to safety concerns. The impact of direct to consumer advertising on drug use seems to be highly variable and probably depends on the characteristics of the advertised drug, the level of exposure to direct to consumer advertising, and the cultural context.
We are grateful to IMS Health Canada, ESI Canada, and Eloda for providing data for this research. We also thank Alyce Adams, Katherine Swartz, Cory Cowan, Ellen Aquilina, Véronique Laramée, Katy Backes Kozhimannil, and Rebecca Anhang-Price for valuable assistance.
Contributors: MRL participated in the design of the study protocol, data collection, statistical analysis, and drafting and revision of the manuscript. SRM participated in the design of the study protocol, data collection, and drafting and revision of the manuscript. SBS participated in the design of the study protocol and drafting and revision of the manuscript. All authors accept full responsibility for the work and/or the conduct of the study, had access to the data, and controlled the decision to publish. MRL is the guarantor.
Funding: MRL is supported by the Thomas O Pyle Fellowship and the Fellowship in Pharmaceutical Policy at Harvard Medical School and by a Social Sciences and Humanities Research Council of Canada doctoral fellowship. SRM receives salary support from the Alberta Heritage Foundation for Medical Research (health scholar) and the Canadian Institutes of Health Research (new investigator). SBS is an investigator in the HMO Research Network Centers for Education and Research on Therapeutics, supported by the Agency for Healthcare Research and Quality (grant No. U18HS010391). The funding and data sources for this study had no role in study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.
Competing interests: None declared.
Ethical approval: The research was appraised and granted an exemption from review by the Harvard Pilgrim Health Care Human Studies Committee.
Provenance and peer review: Not commissioned; externally peer reviewed.
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